The present invention relates to a method for setting up a hybrid tower in an expanse of water, of the type comprising the following steps:                positioning and temporarily retaining a rigid rising column in a substantially vertical configuration in the expanse of water,        totally immersing a buoy for retaining the rising column and displacing the retaining buoy facing the rising column;        inserting a male connecting member borne by a first of the rising column and of the retaining buoy, into a female connecting member borne by a second of the rising column and of the retaining buoy;        immobilizing the male connecting member in a receiving passage defined by the female connecting member        
Such a hybrid tower is for example mounted in an expanse of water such as a lake, a sea or an ocean in order to connect fluid exploitation wells opening out into the bottom of the expanse of water to an assembly for storing and/or discharging this fluid, located at the surface.
For this purpose, the hybrid tower generally comprises a substantially vertical rigid rising column anchored on the bottom of the expanse of water. The rising column is maintained in a vertical configuration by a buoy totally immersed under the expanse of water and attached to the upper end of the column.
A flexible member connects the upper end of the rising column to the surface assembly.
The fluid to be exploited is thereby conveyed between the bottom of the expanse of water and the surface, successively through the rising column and the flexible pipe.
Such a hybrid tower is generally set up in the expanse of water by first of all positioning on the bottom of the expanse of water, a lower connecting assembly comprising a foundation, such as a suction pile or a gravity baseplate and a bent connecting joint which is mounted at the end of an exploitation line stemming from the fluid wells.
And then the rising column, provided with an upper connecting joint is immersed in the expanse of water and is positioned in a vertical position. It is then maintained temporarily in a vertical position by mooring to the laying surface ship.
This column is for example lowered by a so-called J-laying method or by an S-laying method. Alternatively, this column may be made onshore and towed onto the installation site before being immersed.
Next, the retaining buoy is immersed and then tilted into the vertical position, before connecting it onto a connecting joint at the upper end of the rising column.
For this purpose, the connecting means between the buoy and the rising column for example comprise a rod borne by the buoy, and connected to the latter through a chain, and a mandrel for tightening the rod, borne by the rising column. During the connection of the buoy, the rod is introduced into the mandrel before being immobilized in position.
The floatability of the buoy generates a force pulling the rising column upwards, which retains the pipe in its vertical configuration. The temporary mooring means on the laying ship are then released.
Such a method does not give entire satisfaction. Indeed, the connection of the buoy on the rising column is carried out in an immersed medium at several tens of meters under the sea level. As the high portion of the rising column is subject to currents and to swell, it generally oscillates around a vertical central position.
Further, the buoy is often very bulky, since the hybrid towers are capable of having a height of more than 1,500 meters. Thus the buoy should have a diameter of more than several meters for a height of several tens of meters. It is therefore very difficult to maneuver it specifically under the expanse of water.